Mass-Independent Sulfur Isotopic Compositions in Stratospheric Volcanic Eruptions

Baroni, Mélanie; Thiemens, M. H.; Delmas, Robert J.; Savarino, Joël

doi:10.1126/science.1131754

Cited by 156 publications

(231 citation statements)

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“…Agung and Mt. Pinatubo eruptions, sulfate is initially positive in both δ 34 S and Δ 33 S. The subsequent change in sign of Δ 33 S is associated with a significant decrease of δ 34 S, with a slope (Δ 33 S/δ 34 S) of ∼0.1 (8). Moreover, there is broad agreement in Δ 36 S/Δ 33 S after both Mt.…”

mentioning

confidence: 66%

“…A series of groundbreaking studies has shown that sulfur isotopes in sulfate from Plinian eruptions show mass-independent fractionation (MIF) (6)(7)(8). Carbonyl sulfide (OCS) is thought to be the main source of background SSA in volcanically quiescent periods (9), and the reactions breaking down OCS, mainly photolysis, show no evidence of sulfur MIF (10)(11)(12)(13).…”

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confidence: 99%

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SO₂photoexcitation mechanism links mass-independent sulfur isotopic fractionation in cryospheric sulfate to climate impacting volcanism

Hattori

Schmidt

Johnson

et al. 2013

Proc. Natl. Acad. Sci. U.S.A.

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Natural climate variation, such as that caused by volcanoes, is the basis for identifying anthropogenic climate change. However, knowledge of the history of volcanic activity is inadequate, particularly concerning the explosivity of specific events. Some material is deposited in ice cores, but the concentration of glacial sulfate does not distinguish between tropospheric and stratospheric eruptions. Stable sulfur isotope abundances contain additional information, and recent studies show a correlation between volcanic plumes that reach the stratosphere and mass-independent anomalies in sulfur isotopes in glacial sulfate. We describe a mechanism, photoexcitation of SO 2 , that links the two, yielding a useful metric of the explosivity of historic volcanic events. A plume model of S(IV) to S(VI) conversion was constructed including photochemistry, entrainment of background air, and sulfate deposition. Isotopologue-specific photoexcitation rates were calculated based on the UV absorption cross-sections of 32 SO 2 , 33 SO 2 , 34 SO 2 , and 36 SO 2 from 250 to 320 nm. The model shows that UV photoexcitation is enhanced with altitude, whereas mass-dependent oxidation, such as SO 2 + OH, is suppressed by in situ plume chemistry, allowing the production and preservation of a mass-independent sulfur isotope anomaly in the sulfate product. The model accounts for the amplitude, phases, and time development of Δ 33 S/δ 34 S and Δ 36 S/Δ 33 S found in glacial samples. We are able to identify the process controlling mass-independent sulfur isotope anomalies in the modern atmosphere. This mechanism is the basis of identifying the magnitude of historic volcanic events.A ttribution of climate change relies on our understanding of natural climate variation. Volcanoes affect climate, but it is not easy to use proxy records to derive the climate impact of a given historical eruption, primarily because we lack knowledge about the volcanoes themselves. Some so-called Plinian eruptions penetrate the stratosphere, resulting in multiyear climate impacts (1). Volcanic sulfur dioxide (SO 2 ) in a plume is photooxidized in the atmosphere. In the troposphere, the sulfuric acid product is washed out as sulfate in acid rain in a matter of weeks. A Plinian eruption, in contrast, intensifies the stratospheric sulfate aerosol (SSA) layer (2), increasing the planet's albedo (3) and enhancing midlatitude O 3 depletion (4) for more than a year. Ice core records of sulfate provide an important record of volcanic activity (5), but the concentration of sulfate alone does not indicate the explosivity of the event and specifically, if the plume penetrated the stratosphere (6).A series of groundbreaking studies has shown that sulfur isotopes in sulfate from Plinian eruptions show mass-independent fractionation (MIF) (6-8). Carbonyl sulfide (OCS) is thought to be the main source of background SSA in volcanically quiescent periods (9), and the reactions breaking down OCS, mainly photolysis, show no evidence of sulfur MIF (10-13). MIF is not seen at the sour...

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confidence: 66%

mentioning

confidence: 99%

SO₂photoexcitation mechanism links mass-independent sulfur isotopic fractionation in cryospheric sulfate to climate impacting volcanism

Hattori

Schmidt

Johnson

et al. 2013

Proc. Natl. Acad. Sci. U.S.A.

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“…Laboratory experiments have demonstrated that the S-MIF originates during SO 2 photolysis at short wavelengths (λ < 300 nm), producing sulfate with positive Δ 33 S and negative Δ 36 S values, and a wide array of slopes (Δ 36 S/Δ 33 S), ranging from −1.1 to − 4.3 depending on wavelength (12), pressure, and composition of the gaseous mixture (13) . The observations suggest that the S-isotope anomaly in sulfate aerosol in 1998-1999 is a consequence of SO x (SO 2 , SO 3 ) photochemistry (5,6,12,14) in the short UV (<200 nm) region of the solar spectrum above the ozone layer (>25 km) where this wavelength is available in the present-day atmosphere, as will be discussed. The S-isotopic anomalies observed in volcanic sulfate aerosols are accompanied by a significant increase in sulfate concentration (4,5,11).…”

Section: Significancementioning

confidence: 93%

“…The observations suggest that the S-isotope anomaly in sulfate aerosol in 1998-1999 is a consequence of SO x (SO 2 , SO 3 ) photochemistry (5,6,12,14) in the short UV (<200 nm) region of the solar spectrum above the ozone layer (>25 km) where this wavelength is available in the present-day atmosphere, as will be discussed. The S-isotopic anomalies observed in volcanic sulfate aerosols are accompanied by a significant increase in sulfate concentration (4,5,11). The Pinatubo and Cerro Hudson eruptions in 1991 produced a factor of 3.7 sulfate concentration increase in the snow record.…”

Section: Significancementioning

confidence: 93%

“…The Smithsonian database of global volcanic eruptions (www.volcano.si.edu) and Stratospheric Aerosol and Gas Experiment II (SAGE II) archives (18), however, do not list any significant plinian volcanic activity in 1998-1999, ruling out volcanic SO 2 input to the stratosphere as a source for the observed positive S-isotopic anomaly. Increased SO 4 concentrations from local (Antarctic) sources is ruled out because sea salt sulfate and sulfate produced from DMS oxidation is isotopically normal (5,6). A potential new source of the increase in sulfate concentration and S-isotopic anomaly could be the higher altitude transport of SO 2 and potentially from carbonyl sulfide (COS) by deep convection to the tropical tropopause layer, followed by SO 2 photochemistry upon stratospheric COS oxidation (19).…”

Section: Significancementioning

confidence: 99%

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Large sulfur-isotope anomaly in nonvolcanic sulfate aerosol and its implications for the Archean atmosphere

Shaheen

Abaunza

Jackson

et al. 2014

Proc. Natl. Acad. Sci. U.S.A.

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Significance The highest S-isotope anomaly is observed in a nonvolcanic period, and the magnitude of anomaly is similar to the largest volcanic eruptions of the 20th century. S-quadruple isotope data provided the first evidence of how super El Niño Southern Oscillation (ENSO) events (1997–1998) have affected the transport and transformation of aerosols to the stratosphere; thus, record of paleo-ENSO events of this magnitude can be traced with the S-isotopic anomaly. High-resolution and high-precision S-isotopic fingerprinting also revealed that the tropospheric sulfate produced during fossil-fuel and biomass burning contributes to the stratospheric sulfate aerosol layer, a contribution previously unrecognized. The distribution of sulfur anomalies mimics the Archean isotope record, which is used to track the origin and evolution of oxygen on earth.

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Comment on “Climatic impact of the long‐lasting Laki eruption: Inapplicability of mass‐independent sulfur isotope composition measurements” by Schmidt et al.

et al. 2014

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Schmidt et al., in "Climatic impact of the long-lasting Laki eruption: Inapplicability of mass-independent sulfur isotope composition measurements," question the data and the methodology of Lanciki et al. [2012] and disagree with the conclusions by Lanciki et al. regarding the climatic aftermath of the Laki eruption. Here we respond to the issues and questions raised by Schmidt et al. and discuss the disagreements about our conclusions in Lanciki et al. [2012] (hereafter abbreviated as LA2012). (Figure 1 in LA2012) appears to be more than 6 months. We measured the annual layer thickness (from the minimum of one Ca cycle to the next) of a period of 20 years (1772-1801) encompassing the Laki signal and obtain an average annual layer thickness of 28.0 cm snow, with a standard deviation of 6.8 cm. Therefore, the standard deviation of the calculated length (12 months) of the average year is 2.9 months (= (6.8/28.0) × 12). The duration of the Laki sulfate peak is 24.0 cm. This would correspond to a 10.3 month duration for the Laki peak. However, the higher part of the peak, i.e., where the sulfate concentration exceeds the background by 100 ppb, covers 15.0 cm, corresponding to a duration of 6.4 months with a standard deviation of 1.6 month (= 2.9 × 15.0/28.0). Therefore, we believe that the LA2012 statement that the residence time of the bulk of the Laki aerosols did not exceed 6 months is supported by the ice core data.A residence time of less than 6 months for Laki aerosols, according to Greenland ice core data, is not new, nor is it limited to measurement in ice cores from Summit. For example, Wei et al. [2008] presented ice core data from multiple Greenland locations and, after examining the details of the Laki sulfate peaks and the deposition timing of other chemical indicators (Cl, Na, Cd, Bi, etc.) in ice, reached the conclusion of "a short residence time (<6 months) for most of the emissions from Laki," which is the same as that in LA2012.At Summit, Greenland, the deposition durations are 17 months for both the 1815 Tambora and 1809 Unknown eruptions [Cole-Dai et al., 2009], two confirmed low-latitude stratospheric eruptions. The atmospheric residence time of Laki aerosols of 6.4 months (or 10.3 months if the duration of the Laki sulfate signal is estimated from the baseline before to the baseline after the event) is significantly shorter. Timing of the Beginning of the Laki SignalSchmidt et al. raise (paragraph 20) "issues" with "the age model" used in LA2012, by pointing out that "the Laki sulfate peak appears (Figure 1 in LA2012) to start in early spring 1783 when it is expected to start in early summer 1783 (because the Laki eruption commenced on 8 June 1783)." This appearance can be explained by a number of factors in snow accumulation/stratigraphy, ice core data and dating procedures. First, the assignment of time (e.g., Spring, Summer, etc.), based on the appearance of the Ca annual cycle in this case, is approximate. In general, the annual Ca peak appears in spring (April-June); but it is not poss...

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Mass-Independent Sulfur Isotopic Compositions in Stratospheric Volcanic Eruptions

Cited by 156 publications

References 22 publications

SO₂photoexcitation mechanism links mass-independent sulfur isotopic fractionation in cryospheric sulfate to climate impacting volcanism

SO₂photoexcitation mechanism links mass-independent sulfur isotopic fractionation in cryospheric sulfate to climate impacting volcanism

Large sulfur-isotope anomaly in nonvolcanic sulfate aerosol and its implications for the Archean atmosphere

Comment on “Climatic impact of the long‐lasting Laki eruption: Inapplicability of mass‐independent sulfur isotope composition measurements” by Schmidt et al.

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Mass-Independent Sulfur Isotopic Compositions in Stratospheric Volcanic Eruptions

Cited by 156 publications

References 22 publications

SO2photoexcitation mechanism links mass-independent sulfur isotopic fractionation in cryospheric sulfate to climate impacting volcanism

SO2photoexcitation mechanism links mass-independent sulfur isotopic fractionation in cryospheric sulfate to climate impacting volcanism

Large sulfur-isotope anomaly in nonvolcanic sulfate aerosol and its implications for the Archean atmosphere

Comment on “Climatic impact of the long‐lasting Laki eruption: Inapplicability of mass‐independent sulfur isotope composition measurements” by Schmidt et al.

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SO₂photoexcitation mechanism links mass-independent sulfur isotopic fractionation in cryospheric sulfate to climate impacting volcanism

SO₂photoexcitation mechanism links mass-independent sulfur isotopic fractionation in cryospheric sulfate to climate impacting volcanism